Add Kubernetes auth providers (#2147)

* Import auth providers for K8s

* Vendor updates for K8s auth providers

* Remove Azure since it is not compiling

* Update vendor to remove Azure dependencies

vendor/cloud.google.com/go/RELEASING.md

@@ -0,0 +1,13 @@
+# How to Release this Repo
+
+1. Determine the current release version with `git tag -l`. It should look
+   something like `vX.Y.Z`. We'll call the current
+   version `$CV` and the new version `$NV`.
+1. On master, run `git log $CV..` to list all the changes since the last
+   release.
+1. Edit  `CHANGES.md` to include a summary of the changes.
+1. Mail the CL containing the `CHANGES.md` changes. When the CL is approved, submit it.
+1. Without submitting any other CLs:
+   a. Switch to master.
+   b. Tag the repo with the next version: `git tag $NV`.
+   c. Push the tag: `git push origin $NV`.